Transmissible Murine Colonic Hyperplasia (TMCH) is a spontaneous disease of mice characterized by mucosal hyperplasia with minimal inflammatory change. It has a number of potential uses as an animal model of preneoplastic and neoplastic lesions of the human colon. The disease is caused by a bacteria which induces the disease within 2 weeks after inoculation of both conventional and germ-free mice. Kinetic studies indicate markedly increased mitotic activity throughout the entire width of the mucosa including surface epithelium. The length of the cell cycle is prolonged, as is found in neoplasia. Studies are planned to further elucidate cell kinetics by autoradiography, specifically the mitotic index and cell migration rates. Potential synergism of TMCH with chemical carcinogens will be determined. The mode of action of the causative bacteria will be explored by direct multiple intrarectal instillation of killed bacteria or bacterial byproducts. Preliminary experiments investigating the mode of regression of TMCH will be performed, to determine if the mechanism is immunological, or due to bacterial interaction within the gut. Sequential changes in ultrastructure will be correlated with other data.